Field of the Invention
There are a variety of imaging techniques that have been used to diagnose disease in humans. One of the first imaging techniques employed was X-rays. In X-rays, the images produced of the patients' body reflect the different densities of body structure. To improve the diagnostic utility of this imaging technique, contrast agents are employed to increase the density between various structures, such as between the gastrointestinal tract and its surrounding tissue. Barium and iodinated contrast media, for example, are used extensively for X-ray gastrointestinal studies to visualize the esophagus, stomach, intestines and rectum
Ultrasound is another imaging technique In ultrasound, sound is transmitted into a patient via a transducer. When the sound waves propagate through the body, they encounter interfaces from tissues and fluids in the body, and the ultrasound sound waves are either reflected or absorbed. When sound waves are reflected by an interface they are detected by the receiver in the transducer and processed to form an image. The acoustic properties of the tissues and fluids within the body determine the contrast which appears in the resultant image. Contrast agents have been sought which will increase the acoustic difference between the target area and the surrounding area. For example, heavy metals have been tested as contrast agents for ultrasound.
Magnetic resonance imaging (MRI) is a relatively new imaging technique which, unlike X-rays, does not utilize ionizing radiation. As in computed tomography, MRI can make cross-sectional images of the body, however, MRI has the additional advantage of being able to make images in any scan plane (ice, axial, coronal, sagittal or orthogonal). Unfortunately, the full utility of MRI as a diagnostic modality for the body is hampered by the lack of effective contrast agents. Contrast agents have been developed for MRI to improve detection of disease, but most of these efforts have been directed to using chelates of paramagnetic ions as contrast agents. Traditionally employed chelates have the disadvantage of decreasing the relaxivity of the chelate ion as well as potentially causing toxicity, should the metal ion escape from the chelate. Such chelates have the further disadvantage that they are rapidly cleared by the kidneys and do not work as effective contrast agents for imaging of the liver, for example. If better contrast agents were available, the overall usefulness of MRI as an imaging modality would improve.
New and/or better contrast agents for use in X-ray, ultrasound and MRI imaging, and in other imaging systems, are needed. The present invention is directed to these and other important ends.